1. Field of the Invention
The invention relates to a method and equipment for transmitting and receiving data through a mobile station network by using a data terminal device, such as personal computer, connected to a digital mobile station via a standard serial port.
2. Description of the Prior Art
A traditional modem is an electronic device intended to adapt the different data transmission features of the terminal device and the telephone network to one another. These features can deviate from one another with respect to, e.g., the signal type (analog/digital), voltage level, speed of data transmission, and data protocols. The data transmission protocols here refer to the standardized methods applied by the devices participating in the data transmission for ensuring the operation and reliability of the communications. Error correction could be mentioned as an example of the data transmission protocols, for which the transmitting device adds supervisory signals to the data to be transmitted, according to any applicable standard. By comparing the received data with the supervisory signals, the receiver is capable of determining whether errors have occurred in the data transmission.
The traditional modem is connected to the serial port of the terminal. The implementation of the device varies depending on which physical bus the device is connected to the terminal. A computer is herein handled as the terminal, by way of example, comprising an application program, such as a telefax program that uses a modem. According to FIG. 1 modem 1 can be an external device connected to the serial port of terminal 4 and to fixed telephone network 2 by using cable 3. So-called card modem 5 can also be connected directly to the internal bus of computer 4 (FIG. 2) or, especially in portable computers, to the PCMCIA connection (Personal Computer Memory Card International Association). The term "modem" refers to a device intended for communications in a fixed, analog telephone network in particular. Device 7 according to FIG. 3, implementing the tasks of the modem in a digital mobile phone network, is called data adapter. Since the present invention relates mainly to data transmission through a digital mobile phone network, the arrangement according to the invention for data transmission from the terminal to a mobile station operating in a mobile phone network is called a data adapter here. Independent of its physical mode of implementation, the computer handles the traditional modem or the data adapter in digital telephone networks as a serial port from the point of view of data transmission, i.e., as COM-port 9 in PCs (FIG. 4). FIG. 4 presents modem 10 as an example but the traditional data adapter communicates in a completely corresponding way with application program 8 of the computer, through serial port 9 (the COM-port in PCs). Directed by the application program, the computer writes outgoing data D/out into modern 10 and from there into telephone network 2, in the selected serial port 9, and reads incoming data D/in from the serial port. As a separate electronic device modem handles the transferred data and the terminal does not have access to the signal going from the modem to telephone network 2 or coming from the telephone network to the modem. The computer or corresponding terminal provides the modem or data adapter with operating commands and settings by using so-called AT-commands (AT in FIG. 4) by writing them that in serial port 9 in which modem 10 or the data adapter are visible. The responses to the commands given by the modem or the data adapter to the terminal can also be read in the serial port in question. For the writing and reading of the commands, modem 10 or the data adapter must be in the so-called command state, and the term AT-command is derived from the fact that, according to general practice, all the commands given to the modem or to the data adapter begin with letters AT.
The processor of the computer does not communicate directly with physical port 9, controlled by application program 8, but port controller 11 is placed inbetween, implemented in the computer preferably as a port controller program (FIG. 5). Port controller 11 contains the data on which address of the memory space the UART-circuit 12 (Universal Asynchronous Receiver Transmitter) controlling the desired port is located in and which interrupt signal it uses, but the ordinary port controller does not process data going through it. There is a direct connection from UART-circuit 12 to the connector of serial port 9. The standard connector (e.g., RS-232) of the serial port comprises respective lines for incoming and outgoing asynchronous data and so-called handshake lines for controlling the data transmission. If the modem or data adapter 7 is connected, as in FIG. 6, to the internal bus of computer device 4 or to a PCMCIA connection, the transmitted and received data travels via UART-circuit 15 inside the modem or the data adapter, instead of the respective UART-circuit of the computer. In the case of FIG. 6, the tasks of the modem are handled by data adapter card 7 because the data transmission is effected in a digital mobile phone network.
Disadvantages of the traditional modem and data adapter are that it is a separate electronic device which must be acquired and installed in the computer before data can be transmitted through the telephone network. When installed, the modem or data adapter reserves one serial port and, in the case of the card modem an expansion slot, and in the case of the PCMCIA data adapter a PCMCIA interface, which, consequently, cannot be used with other auxiliary devices any more. Since the modem and the computer are generally not manufactured by the same company, different mechanical and electric tolerances and performance characteristics as well as actual factory defects can cause disturbance in the interworking of the computer and the modem, despite all standardization efforts.
The modem or data adapter generally contains adjustable selections or switches that have to be set properly before it is installed in the computer and that are difficult to modify. The structure and components of the modem can restrict its use in different operating modes, and if changes are made in the data transmission protocols, parts of the modem or even the whole modem might have to be replaced. The modem and telephone set have to be linked by a special cable which generally does not conform to any standard connections found in computers.